Genetic programming with Objective-C
I have not touched Obj-C, but I've played with evolution in PHP, which wasn't designed for that at all. If a slow script language on my 10-year old desktop PC can do it, Obj-C should be able to handle that.

Some tricks:


This is a game, so - I assume - you've disabled all the graphics. A headless program is ideal for training. Waste no CPU cycles on stuff you don't need!
Use more threads/instances. Threads around the number of cores should be ideal.
Watch out for memory leaks! Even languages with GC can have problems with this when used in a wrong way. But you'll need to fix these bugs anyway. You can monitor memory consumption when you run it, and if it increases more-or-less steadily, that's a problem. There are various tools against memleaks under different systems/languages, I guess Obj-C has something similar. (these tools log every allocation and release, and list everything at exit that's left)